I don't see why the 4.6 damper wouldn't work fine.
I have compared the many dampers I have at my shop, and they all look interchangable. If somebody has some different info, I hope they chime in.
I have on hand and have compared:
5.4 Lightning 8 rib - Using it on my 5.4 4v Eaton conversion (only using 6 rib belt for accessories for right now, maybe switch to 8 rib later)
4.6 Terminator 6 rib
5.4 Truck 8 rib
5.4 Truck 6 rib
5.4 Nav 4v 8 rib
5.4 Nav 4v 6 rib
4.6 2v 6 rib